1. Field of the Invention
The present invention relates to a parking brake control unit that performs lock control of an electric parking brake (EPB).
2. Description of the Related Art
Generally, parking brakes are used to restrict the movement of parked vehicles. Various parking brakes are known, such as, for example, manual parking brakes that transmit an operation force to a brake mechanism by pulling a brake cable using a control lever, and electric parking brakes that transmit motor torque to a brake mechanism by pulling a cable using the torque of the motor.
When an electric parking brake (EPB) is locked, a motor is rotated to a locked side (positive rotation) so as to transmit the motor torque to a brake mechanism (an actuator), and the motor drive is stopped in a state where a brake force is generated. When the EPB is released, the motor is rotated to a released side (negative rotation) so as to release the brake force.
Among the EPBs in which lock/release control like that described above is performed, an EPB is disclosed that uses an automatic pressurizing function of a service brake in order to reduce motor output when the parking brake is applied. More specifically, when a vehicle is stopping on a flat road with a relatively small load and a large brake force does not need to be generated, only a motor for the parking brake is actuated. When the vehicle is stopping on a sloped road with a relatively large load and a large brake force needs to be generated, the service brake compensates for insufficient brake force of the parking brake. Thus, brake force that is sufficient to prevent the vehicle from sliding down is secured (refer to JP-T-2007-519568, for example).
However, when the service brake compensates for the insufficient brake force of the parking brake as described in JP-T-2007-519568, the magnitude of the service brake application, namely, the brake force generated by a driver depressing a brake pedal is not taken into consideration. Therefore, when the driver depresses the brake pedal with a large depression force, there is a possibility that the brake force generated when the parking brake is applied will be larger than necessary. In this case, the durability of a brake caliper and a parking brake actuator needs to be set such that, even when a large brake force is generated, the brake caliper and the parking brake actuator can endure it. As a result, tough requirements need to be satisfied, and the size and weight of the brake caliper and the parking brake actuator are increased.